1. Field of the Invention
The present invention relates to materials processing and, more particularly, relates to forming electrons from tungsten leads.
2. Related Art
Welding a first tungsten component to a second tungsten component to form an assembly generally is not considered to be feasible because the welding operation itself causes severe recrystallization of the tungsten adjacent to the melted area, i.e., the weld, between and formed by the components. This recrystallization of the tungsten causes the tungsten components to become brittle and results in a weak bond. As used herein, the term "tungsten component" refers to components composed of tungsten, alloys of tungsten, tungsten alloys including a solid suspension, tungsten including a solid suspension, or any combination of materials including tungsten.
Moreover, problems associated with welding tungsten components to other tungsten components are amplified when the tungsten components to be welded are an electrode, such as an anode, and a lead. The term "lead", as used herein, refers to an electrical conductor for conducting electricity to an electrode. The end portion of the lead which is to be bonded to the end portion of the anode typically has a very small diameter. The lead, for example, has a diameter of 0.0165 inches and the anode has a diameter of 0.040 inches. Providing a strong bond between such small working areas is very difficult.
It is known to join tungsten components to other tungsten components by brazing. Particularly, the tungsten components are aligned and held in contact at a location where a bond is to be formed. The brazing metal is then melted at the location where the bond is to be formed. The brazing metal, however, typically has a lower melting temperature than the melting temperature of tungsten. As a result of the difference between the melting temperature of the brazing metal and the tungsten, a strong bond between the tungsten components and the brazing metal is not present when the components, in operation, are subjected to elevated temperatures near the braze material melting point. Brazing techniques, therefore, do not provide sufficient bond strength between the tungsten components at elevated temperatures close to the brazing material melting point. The brazing metal may also be a source of contamination in some applications.
To overcome these problems, a method for forming an anode-lead assembly by melting back the end of a lead can be utilized. The end of the lead typically is melted with a tungsten-inert-gas (TIG) welder. When the end of the lead i smelted, a spherical-shaped portion having a larger diameter than the other portion of the lead is formed. Particularly, when the tungsten is melted, the melted tungsten forms into the spherical-shape due to surface tension. The spherical-shaped portion serves as an anode. In the TIG operation, it is difficult to control the diameter of the anode, i.e., the diameter of the spherical-shaped portion, being formed. Further, in some applications, the spherical-shape of the anode is unsatisfactory such as too large or of undesirable shape. For example, it may be preferred that the anode be bullet-shaped or conically-shaped.
One known technique to shape the anode formed by the TIG process is commonly referred to as electrical discharge machining (EDM). Particularly, subsequent to a TIG process, EDM techniques are used to cut the desired anode shape from the spherical-shaped portion of the melted lead. EDM techniques, however, typically require tens of minutes to complete and are too slow to be cost effectively used in mass production of such assemblies. Other techniques for shaping the anode such as machining and etching also require too much time and result in waste.
In commonly assigned copending U.S. patent application Ser. No. 07/622,037, "Apparatus For Welding Components", an apparatus that can be used to weld tungsten components is described. One embodiment of an apparatus in accordance with the invention described in the copending patent application comprises means for aligning the first component and the second component, means for heating at least a portion of the first component, and means for forcing the second component within a melt formed as a result of heating the first component. The heating means, in the exemplifications embodiment, is at least a first laser beam. Particularly, in the exemplification embodiment, the laser beam is a laser beam pulse emitted by a neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) source and the laser beam pulse has a wavelength of 1.06 micrometers. The beam pulse is directed, for example, at a portion of the first component. The energy from the laser beam is absorbed by the first component and causes at least a portion of the first component to form a melt. It is contemplated, of course, that sources of energy other than a laser can be utilized. The energy source preferably provides highly focussed energy which generates, when absorbed, localized heat in the tungsten component.
In commonly assigned copending U.S. patent application Ser. No. 07/622,080, "Method For Welding Components", a method for welding tungsten components is described. One embodiment of a method in accordance with the invention is described in the copending patent application includes the steps of aligning the first component and the second component so that a first portion of the first component is disposed substantially adjacent a first portion of the second component, and heating at least a portion of the first component. As the first component is heated, a melt is formed at the first portion of the first component. The first portion of the second component is forced into and maintained within the melt. As the melt solidifies, a strong bond is formed between the first and second component.
The heating, in the exemplified embodiment, is provided by at least a first laser beam. Particularly, in the exemplification embodiment, the laser beam is a laser beam pulse emitted by a neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) source and the laser beam pulse has a wavelength of 1.06 micrometers. The beam pulse is directed, for example, at a portion of the first component. The energy from the laser beam is absorbed by the first component and causes the melt to form. It is contemplated, of course, that sources of energy other than a laser can be utilized. The energy source preferably provides highly focussed energy which generates, when absorbed, localized heat in the tungsten component. The components to be welded could be composed of materials other than tungsten or some combination of materials including tungsten.
The above described apparatus and method can be used to weld the small working areas of a tungsten electrode and a tungsten lead. The resulting bond is a strong bond and does not result in damage to the components. Moreover, operations are performed relatively fast which facilitates mass production of the anode-lead assemblies.
It would be desirable, of course, to even further reduce the time required to form an electrode-lead assembly, and to simplify the process of forming the assembly. For example, in a welding operation, typically a relatively complex apparatus is used to hold the electrode and the lead. Eliminating a need for such a complex apparatus would be desirable, for example, because processing costs would be reduced.
It is therefore an object of the present invention to provide a method for forming an electrode-lead assembly.
Another object of the present invention is to provide a method for forming an electrode-lead assembly which eliminates a need for complex apparatus.
Still another object of the present invention is to provide a method for forming an electrode-lead assembly which facilitates reducing processing time.
Yet another object of the present invention is to provide a method for forming an electrode-lead assemble which is simple and easy to perform.